Multiplexed tri-mode visual outputs of immunoassay signals on a clip-magazine-assembled photothermal biosensing disk

The photothermal biosensing principle is of increasing interest for point-of-care detection, but has rarely been applied in portable analytical devices in a lab-on-a-chip format. Herein, a photothermally responsive poly (methyl methacrylate) (PMMA)/paper hybrid disk (PT-Disk) was developed as a novel photothermal immunoassay device with the integration of a clip-magazine-assembled photothermal biosensing strategy. The PT-Disk consisted of a dissociative thermoresponsive hydrogel-loaded clip unit where the sandwich-type immunoreaction with an iron oxide-to-Prussian blue nanoparticle (PB NP) conversion took place and a magazine bearer for the rotational clip assembly and visual signal outputs. Upon laser irradiation of the clip-magazine-assembled PT-Disk, on-chip photothermal effect of PB NPs triggered both dose-dependent temperature elevation and the subsequent release of dye solutions from the central clip unit to surrounding magazine-bearing paper channels as the result of phase transition of the hydrogels, realizing multiplexed thermal image- and distance-based visual quantitative signal outputs in combination with the preliminary colorimetric readout on the PT-Disk. Using the multiplexed tri-mode signal outputs, the PT-Disk can quantify prostate specific antigen with limits of detection of 1.4-2.8 ng mL^-1. This is the first attempt to apply the photothermal biosensing principle in portable PMMA/paper-based analytical devices, which offers not only versatile on-chip visual quantitative signal outputs, but also the implementation of the photothermal biosensing principle in a lab-on-a-chip format.